With age, a large percentage of the population develops atherosclerotic arterial obstructions resulting in diminished blood circulation. The disturbance to blood flow that these obstructions cause may induce blood clots which further diminish or block the blood flow. When this process occurs in the coronary arteries it is referred to as a heart attack. Presently such obstructions are circumvented by surgically grafting a bypass or they are treated by a catheter equipped with a hydraulically expandable tubular element (balloon), made from a non-stretchable thin plastic material which is inserted through the arterial system, over a flexible guide-wire, into the obstruction and then inflated to expand the obstruction""s lumen. Some of the problems with balloon catheters are that they tend to tear the arterial wall in an uncontrolled manner along a line of least resistance (which is often a less diseased side of the artery since arterial disease is rarely symmetrical as viewed in an arterial cross section). In extreme cases such uncontrolled tearing of the artery can progress through all the layers of the arterial wall cracking it open and causing an internal bleeding.
An objective of the present invention is to provide an improved hydraulically expandable catheter for insertion into the obstruction which is made of a hydraulically expandable tube that generally has a clover leaf shape in its relaxed, deflated, position. The expandable tube has longitudinal ridges attached to it that are harbored in the folds of the clover leaf shape and, when the expandable tube is inflated to become substantially circular, the ridges part the obstruction material along multiple lines as they are displaced radially outward and are pushed into the material.
A further objective is to prepare the obstruction site for a follow-up treatment with an atherectomy system (as shown for example in my cross-referenced parent applications) or for placing a stent (as shown for example in U.S. Pat. No. 4,503,569 issued on Mar. 12, 1985 or U.S. Pat. No. 4,886,062 issued on Dec. 12, 1989).
A further objective is to provide a ridge made of a series of interconnected elements so that it is flexibly bendable (along its longitudinal axis) but still has a rigid cross section that will not cave-in when pushed into the surrounding obstruction material.
A further objective is to provide a ridge having a parting edge that is pointed away from the obstruction material when the expandable tube is in its relaxed, deflated, position. This makes the catheter less likely to cause any damage while it is advanced, or retracted, from the obstruction site while maximizing the effectiveness of the edge as it is pushed into the obstruction material. When the expandable tube is inflated, the change in the expandable tube""s cross section from a clover leaf shape to a substantially circular shape is utilized to turn the edge towards the obstruction material.
A further objective is to provide a ridge having a parting edge that is recessed in the ridge and less likely to contact the expandable tube when the expandable tube is in its relaxed position. This also makes the parting edge less likely to cause any damage to the vasculature or to soft parts of the catheter while it is advanced, or retracted, from the obstruction site. When the expandable tube is inflated, the change in the expandable tube""s cross section from a clover-leaf shape to a substantially circular shape is utilized to bring the parting edge out of the ridge towards the obstruction material.